Resin board, manufacturing process for resin board, connection medium body, circuit board and manufacturing process for circuit board

ABSTRACT

A compression function layer  60  is provided on at least one board surface. The compression function layer  60  adds a function of being compressed by receiving pressure in the direction of the board thickness to the resin board  10  which includes this layer. Thereby a sufficient pressure is applied to conductors  14.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin board which is used as acircuit board, a connection medium body, a manufacturing process for aconnection medium body a circuit board and a manufacturing process for acircuit board.

2. Description of the Related Art

In recent years, together with the miniaturization, reduction of weight,increased functionality and increased performance of electronic devices,the demand has become strong, concerning industrial application as wellas concerning application in the broad field of consumer devices, for amulti-layer circuit board on which semiconductor chips such as LSIs canbe mounted in high density at an inexpensive price.

A resin multi-layer circuit board which can be supplied less expensivelythan a ceramic multi-layer board and which can fulfill the abovedescribed market demand has attracted attention as a substitute for aconventional ceramic multi-layer board and technological development hasbeen carried out to develop a resin multi-layer circuit board that is aboard suitable for high density mounting.

As a resin multi-layer circuit board developed in this manner, a circuitboard of an any layer inner via hole construction has been disclosed inJapanese Unexamined Patent Publication No. Hei 06-268345 (1994). Thiscircuit board is a resin multi-layer board using a composite material ofaramid non-woven fabric reinforcing material and an epoxy resin as theinsulating layer and, therefore, can be supplied at a comparativelyinexpensive price. In addition, this circuit board adopts the any layerinner via hole construction, that is to say, an interstitial via holeconnection construction which can connect arbitrary positions in wiringlayers through conductive paste and, therefore, becomes suitable forhigh density mounting.

A circuit board of the any layer inner via hole construction having theabove characteristics cannot be formed unless a prepreg is used whichhas voids in the inside due to the impregnation of resin into anon-woven fabric. That is to say, this circuit board has a constructionwhich can be implemented only by using a particular material.

However, in addition to a higher density of mounting, today, marketdemands have become as follows. That is to say, market demands aremanifold and there are demands such as a circuit board of a lowdielectric constant suitable for a high speed circuit network, a circuitboard of a high heat resistance, and the like. Therefore, it is requiredto implement a circuit board which has characteristics that fulfillrespective desires and suitable for high density mounting.

SUMMARY OF THE INVENTION

Accordingly, the main purpose of the present invention is to provide acircuit board which can implement a low connection resistance and anexcellent connection stability.

In order to achieve the above described purpose, the present inventionprovides a compression function layer on at least one board surface togain a resin board used in an insulating layer of a circuit board or aconnection medium body. The compression function layer hascharacteristics such that it adds the function of being compressed byreceiving pressure in the direction of the thickness to a resin board ora medium connection body.

According to the present invention, a circuit board which adds acompression function and implements a low via connection resistance andan excellent connection stability can be gained without being limited toa specific combination of materials and, rather, can be gained by makingthe surface have specific characteristics.

The compression function layer is preferably a porous layer. Then, bycontrolling the degree of invasion of a resin component of the resinboard into the porous layer, the function of being compressed byreceiving pressure in the direction of thickness can be added to theresin board.

The porous layer has a hole group wherein the hole group is preferablyformed of a plurality of holes which are connected to each other so thatboth ends of the hole group have openings on both sides of the porouslayer. Then, air held in the holes can be ejected to the outside throughpressure in the direction of the board thickness. Thereby, it can bemade easier for the resin component of the resin board to invade intothe porous layer and the amount of invasion of this resin component tothe porous layer can be easily controlled by adjusting the pressure.

The above described compression function layer can also be formed of alayer of insulating particles which is provided on a resin board orconnection medium body in the condition protruding from the boardsurface. In this case, the insulating particles protruding from theboard surface are pressed into the resin board by receiving pressure inthe direction of the board thickness and, thereby, the compressionfunction can be added to the resin board.

The resin board is preferably in a semi-cured condition on, at least,the surface on which the compression function layer is provided. Then,because of the semi-cured condition of the board material, advantagesare gained as follows. That is to say, in the compression function layermade up of a porous layer, it becomes easier for a resin component toinvade into the porous layer. In addition, in the compression functionlayer made up of insulating particles, it becomes easy to pressinsulating particles into the resin board.

The resin board is preferably provided with a protective film layer soas to be removable as an additional layer above the above describedcompression function layer. Thereby, during a manufacturing step for acircuit board using the resin board or the connection medium body, dustfrom the outside can be prevented from becoming attached to thecompression function layer. In addition, the entire thickness of theresin board or the connection medium body can be adjusted through theaddition or removal of a protective film layer. Thereby, it becomespossible to add a compression margin at the time when conductorsprovided through the resin board or the connection medium body in thedirection of the thickness is compressed.

A resin board of the present invention can be manufactured as follows.That is to say, after a porous layer is provided on at least one boardsurface of a resin board, the above described porous layer is adhered tothe above described resin board through pressure by applying pressure tothe above described resin board of the degree that a resin component ofthe above described resin board does not invade into the holes of theabove described porous layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The other purposes of the present invention will become evident byunderstanding the below described embodiments and are clearly shown inthe attached claims. And, those skilled in the art will perceive anumber of advantages that are not touched on in the presentspecification in the case that this invention is implemented.

FIG. 1A is a cross sectional view showing a construction of a resinboard 10A according to the first preferred embodiment of the presentinvention;

FIG. 1B is a cross sectional view showing a construction of a resinboard 10B according to the first preferred embodiment of the presentinvention;

FIG. 2A is a cross sectional view showing a manufacturing process for aresin board 10A;

FIG. 2B is a cross sectional view showing a manufacturing process for aresin board 10B;

FIG. 3A is a cross sectional view showing a construction of a resinboard 30 according to the second preferred embodiment of the presentinvention;

FIG. 3B is a cross sectional view showing a construction of the resinboard 30 in the compressed condition;

FIG. 3C is a cross sectional view showing another construction of theresin board 30;

FIG. 4 is a cross sectional view showing a construction of a resin board50 according to the third preferred embodiment of the present invention;

FIG. 5 is a cross sectional view showing a construction of a connectionmedium body 12 according to the fourth preferred embodiment of thepresent invention;

FIGS. 6A and 6B are cross sectional views respectively showing the stepsin a manufacturing process for a double surface board 17 according tothe fifth preferred embodiment of the present invention;

FIGS. 7A and 7B are enlarged cross sectional views of a main partshowing, respectively, the condition of a resin component 58 flowinginto recesses 51;

FIG. 8 is a plan view showing the relationships between the maximumdiameter L of a hole 104 and the minimum separation interval S ofconductors 14;

FIGS. 9A and 9B are cross sectional views showing, respectively, thesteps in a manufacturing process for a double surface circuit boardusing a wiring layer with carriers;

FIGS. 10A to 10D are cross sectional views showing, respectively, thesteps in a manufacturing process for a double surface circuit board 17using protective film layers;

FIGS. 11A and 11B are cross sectional views showing, respectively, thesteps in a manufacturing process for a multi-layer board;

FIGS. 12A-1 to 12D are cross sectional views showing, respectively, thesteps in another manufacturing process for the double surface circuitboard;

FIGS. 13A and 13B are cross sectional views showing, respectively, thesteps in another manufacturing process for the multi-layer board;

FIGS. 14A to 14C are cross sectional views showing, respectively, thesteps of the first half in still another manufacturing process for themulti-layer board; and

FIGS. 15A and 15B are cross sectional views showing, respectively, thesteps of the second half in the manufacturing process directly above forthe multi-layer board.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the preferred embodiments of the present invention aredescribed in reference to the drawings.

First Preferred Embodiment

FIGS. 1A and 1B are cross section schematic views showing a resin board10 of the present embodiment.

Resin boards 10A and 10B have porous layers 11 on the surfaces. That isto say, the difference between the resin boards 10A and 10B of thepresent embodiment and a conventional resin board is whether or not aporous layer 11 which becomes a compression function layer is placed ona surface and the resin boards 10A and 10B of the present embodimenthave porous layers 11 on, at least, one surface.

Though in the configurations of FIGS. 1A and 1B, the porous layers 11are provided, respectively, on both sides of the boards 10A and 10Bshown as examples, in the case that where a porous layer is provided ononly one side, a resin board of the present invention can be gained.

As for the board material of the resin boards 10A and 10B of the presentembodiment, a prepreg 100 wherein thermosetting resin is impregnatedinto a fiber material for reinforcement or an adhesive sheet 101 can beused. An example wherein the prepreg 100 is used is the resin board 10Ashown in FIG. 1A while an example where the adhesive sheet 101 is usedis the resin board 10B shown in FIG. 1B.

As for the prepreg 100, a glass epoxy prepreg, an aramid epoxy prepreg,or the like, can be cited. The glass epoxy prepreg is gained byimpregnating an epoxy resin in a semi-cured (B stage) condition into aglass non-woven cloth. The aramid epoxy prepreg is gained byimpregnating an epoxy resin in a semi-cured condition into an aramidnon-woven cloth. Here, the epoxy resin in the semi-cured condition hasadhesive properties. Therefore, in these prepregs 100 it is notnecessary to provide an adhesive layer for adhering the porous layer 11to the surface of the prepreg 100 as shown in FIG. 1A.

The adhesive sheet 101 is a film board made of thermoplastic resin or athermosetting resin such as a polyimide, a liquid crystal polymer, anaramid or a PTFE (poly-tetra-fluoro-ethylene). As for the resin board10B made of the adhesive sheet 101, as shown in FIG. 1B, an adhesivelayer 102 made of a thermosetting resin or a thermoplastic resin isprovided on the surface of the adhesive sheet 101 where a porous film isformed.

The types of thermosetting resin or thermoplastic resin (hereinafterreferred to as a prepreg impregnation resin) which are impregnated intothe prepreg 100 or the resins forming the adhesive layer 102 which isprovided to the adhesive sheet 101 can be selected according to thecombinations of the resin boards 10A, 10B and the metal used for wiringlayers (described below) and are not particularly limited.

As described below, however, it is necessary to make an adhesive or aprepreg impregnation resin invade into the inside of the spaces of theporous layers 11 from the surrounding area. In order to make theseresins invade into the porous layers 11, it is necessary for the prepregimpregnation resin or the adhesive layer 102 to maintain fluidity duringthe step. Therefore, in the case of a thermosetting resin, it is used ina semi-cured condition. In addition, in the case of a thermoplasticresin, it is made fluid by adjusting the temperature at the time of thestep wherein the adhesive is made to flow at the softening temperaturepoint, or greater.

As for the concrete materials for the prepreg impregnation resin or theadhesive layer 102, the following can be cited. That is to say, athermosetting resin or a thermoplastic resin such as an epoxy resin, apolyimide resin, a phenol resin, a fluorine resin, an unsaturatedpolyester resin, a PPE (poly-phenylene-ester) resin, a bismaleimidetri-azine resin, a cyanate-ester resin can be cited. Here, in the casethat a film board of a thermoplastic resin is used as the adhesive sheet101, the film board itself has adhesive properties at the softeningtemperature point, or greater and, therefore, the film board itself canalso be made to serve as an adhesive layer.

At least one board surface of the resin board 10A, 10B formed in theabove manner is provided with a porous layer 11. The porous layer 11 isa compression function layer which adds the function of being compressedby receiving pressure in the direction of the thickness to the resinboard 10A, 10B. As for a concrete example of the porous layer 11, aporous sheet of a PTFE (poly-tetra-fluoro-ethylene), a polyimide, anaramid, or the like, or a porous ceramic can be cited.

These porous layers 11 can provide microscopic holes from 1 μm, or less,to several μm in the inside thereof. In addition, in that case the sizeof the holes can be controlled in a highly precise manner.

It is preferable to provide a compression function layer made of theporous layer 11, of which the dielectric constant is small such as aPTFE (poly-tetra-fluoro-ethylene) at the time of the manufacturing of acircuit board used for a high frequency circuit from the followingpoints of view.

That is to say, since the magnetic flux density leaking from the wiringlayer is high, the effect of the dielectric loss of the dielectricconstant is larger in the surface layer portions closest to the wiringlayer of the resin board 10A or 10B than in the inside of the resinboard 10A or 10B. Therefore, in the case that the compression functionlayer of the porous layer 11, or the like, provided in the surfaceportions of the resin board 10A or 10B is formed of a low dielectricconstant material, a high frequency characteristic in a circuit boardmade of the resin board 10A or 10B can be increased. In addition, byproviding the porous layer 11, the mechanical strength of the resinboard 10A or 10B can be reinforced.

The porous layers 11 have a plurality of hole groups 103 in the insidethereof. The hole groups 103 are formed by a plurality of holes 104connected to each other. At least one of these hole groups 103 hasopenings on both sides of a porous layer 11 on both edges thereof, thatis to say, at least one hole group 103 exits from among the hole groups103 which is in a non-sealed condition that is not sealed in the porouslayer 11. Both sides of the porous layer 11 are mutually connectedthrough the hole group(s) 103 formed in the above manner.

Next, manufacturing processes for the resin boards 10A and 10B aredescribed in reference to FIG. 2. FIG. 2A shows a manufacturing processfor the resin board 10A while FIG. 2B shows a manufacturing process forthe resin board 10B.

Manufacturing processes for both of the resin boards 10A and 10B areessentially the same. That is to say, compression function layers arelayered on both sides of the prepreg 100 or on the adhesive sheet 101 soas to be integrated. Concretely, the porous layers 11 are adhered byapplying heat and pressure to both sides of the prepreg 100 or to theadhesive sheet 101. Adhesion by applying heat and pressure can becarried out by, for example, rotating a heated roller in the conditionwhere it is pressed onto the porous layers 11. Here, at the time ofadhesion by applying heat and pressure, the pressure applied to theresin board 10A or 10B is to the degree where the resin components ofthe resin board 10A or 10B hardly invade into the holes 104 of theporous layers 11. Here, the resin components of the resin board 10A or10B mean resin components forming the impregnation resin of the prepreg100 or forming the adhesive layer 102.

At the time when the porous layers 11 are adhered to the resin board 10Aor 10B through pressure, a protective film layer may be simultaneouslyformed so as to be removable on, at least, one board surface of theresin board 10A or 10B. In this case, a porous layer 11 is formed on theprotective film layer in advance and, after the porous layer 11 isarranged so as to contact a side of the resin board 10A or 10B, theprotective film layer is adhered through pressure and, thereby, a resinboard having a protective film layer and a porous layer 11 can bemanufactured simply with a smaller number of manufacturing steps. As forthe conditions of adhesion through pressure at this time, the followingconditions can, for example, be set. That is to say, in the case that aPET film (thickness 4 μm to 25 μm) is adhered to a glass epoxy prepregor to an aramid epoxy prepreg through pressure, the feeding speed of theroller heated to the temperature of 100° C. to 140° C. can be set at 1m/sec to 3 m/sec and the air pressure can be set at 0.5 kgf/cm² to 5.0kgf/cm². The protective film layer and the porous layer 11 may, ofcourse, be formed on both sides of the resin board 10A or 10B. However,an asymmetric arrangement is, of course, possible wherein the porouslayer 11 and the protective film layer are both provided on only one ofthe board surfaces of the resin board 10A or 10B while only theprotective film layer is provided on the other board surface.

Second Preferred Embodiment

A resin board 30 according to the second preferred embodiment of thepresent invention is described in reference to FIG. 3. FIG. 3A is across section schematic view showing the resin board 30 which has aninsulating particle layer 32 that becomes a compression function layer.

The present embodiment is formed in the same manner as the firstpreferred embodiment except for that the porous layers 11 in the firstpreferred embodiment are changed to the insulating particle layers 32.

An insulating particle layer 32 can be formed as follows. That is tosay, by adding a plurality of insulating particles 31 to an adhesivelayer 102′ in the resin board 10B made of the adhesive sheet 101described in the first preferred embodiment, the insulating particlelayer 32 can be formed of this adhesive layer to which the insulatingparticles are added.

As for the details, the insulating particle layer 32 is formed by addinginsulating particles 31 such as silica, alumina or aluminum hydroxide tothe adhesive layer 102′. Then, an insulating particle layer 32 formed inthis manner is formed on, at least, one board surface of the resin board10B. At this time, some insulating particles 31 are in the condition ofprotruding from the surface of the adhesive layer 102′.

In the resin board 30 which has such an insulating particle layer 32, asshown in FIG. 3B, the insulating particles 31 are pressed into theinside of the adhesive layer 102′ in the subsequent heat compressionstep. Thereby, the resin board 30 is compressed.

In the case that a similar insulating particle layer to the abovedescribed insulating particle layer 32 is provided when the resin board30 is formed by using the resin board 10A made of the prepreg 100described in the first preferred embodiment, the following may becarried out.

That is to say, as shown in FIG. 3C, a resin including insulatingparticles 31′ is used for the resin impregnated into a cloth or anon-woven cloth which becomes a reinforcing material in the prepreg 100.As a concrete example of such a resin board 30′, a glass epoxy prepregincluding fillers can be used wherein an epoxy resin in which silicaparticles are diffused is impregnated into a glass cloth.

Third Preferred Embodiment

The third preferred embodiment of the present invention is described inreference to FIG. 4. FIG. 4 is a cross section schematic view showing aresin board 50 which has recesses 51 that function as compressionfunction layers on the surfaces. That is to say, the difference betweenthe resin board 50 of the present embodiment and a conventional resinboard for a circuit board is whether or not a surface has a recess 51and the resin board 50 of the present invention has, at least, onerecess 51 on at least one board surface. Though in FIG. 4 an example isshown wherein a plurality of recesses 51 are provided on both sides, thecase wherein the recesses are provided on only one side or the casewherein only one recess is provided can also be assumed to be the resinboard 50 of the present embodiment.

As described below, the forms or the number of recesses 51 are notparticularly limited but, rather, the total volume of the entirety ofthe recesses becomes important.

As for the material of the resin board 50 of the present embodiment, thesame material as resin boards 10A, 10B and 30 in the first and secondembodiments can be used.

A method for creating the recesses 51 is not particularly limited and,for example, an adhesive layer is formed on a support body on whichprotruding parts corresponding to the recesses 51 are provided and,then, after transcribing the adhesive layer onto a film board, therecesses can be created by removing the support body. As for theadhesive layer, a thermosetting adhesive or a thermoplastic adhesive canbe used. In the case of a thermosetting adhesive, it is transcribed in asemi-cured condition to create recesses while, in the case of athermoplastic adhesive, it is heated to the softening temperature point,or greater, at the time of transcription for creating recesses.

In addition, as for another method for creating recesses 51, there isthe following method. That is to say, a flat adhesive layer is formed ona film board in advance and, by using a metal mold to which protrudingparts are provided corresponding to the positions of the recesses 51,pressure is applied to the mold so as to be pressed to the adhesivelayer in a semi-cured condition. After that, by removing the mold, therecesses 51 of a desired size and shape can be provided on desiredpositions of the adhesive sheet. In addition, in the case of athermoplastic adhesive, the mold is pressed while being heated to thesoftening temperature point, or greater.

It is preferable to carry out a mold releasing process in the parts ofthe above described support body or adhesive layer which contact theadhesive layer. Then, the adhesive becomes easier to be released fromthe support body or from the mold so that manufacturing a resin board 50of the present embodiment becomes easier. In addition, in the method forcreating recesses 51 with the above described support body or mold, theform, the number, the intervals, or the like, of the recesses 51 can bearbitrarily selected.

As for another method for creating recesses 51, there is the followingmethod. That is to say, after preparing a solution wherein athermosetting adhesive is diluted by a solvent, a supersonic vibrationis given to the solution so as to cause bubbles. The solution containingbubbles is applied to a film board. Then, by drying the solutioncontaining bubbles on the film board, the solvent is volatilized to bein a semi-cured condition. Thereby, the bubble portions become holes soas to create the recesses 51.

As for an example of such a method, there is the following method. Thatis to say, a supersonic vibration (38 kHz, 150 W) is given to a THF(tetra-hydroxy-furan) solution (30 wt % of solids) of a polyimide-basedadhesive so that bubbles are caused. Then, the solution is applied to afilm board 13 μm thick) made of polyimide by a gap coater and is driedfor one minute at 120° C. Thereby, recesses 51 are formed in the driedsolution. The thickness of the solution after being dried isapproximately 6 μm.

Furthermore, as for another method for creating recesses 51, there isthe following method. That is to say, a light sensitive adhesive layeris formed in a flat manner on a film board in advance. This adhesivelayer is covered with a mask which corresponds to the recesses 51 of adesired form and size followed by exposure for developing the non-curedportions. Thereby, recesses 51 are created in the adhesive layer. Inthis case, the adhesive layer is left in a semi-cured condition.According to this method recesses 51 can be created in a comparativelyeasy manner.

In the case of a resin board 50 made of a prepreg, recesses 51 can becreated by a similar method to a resin board made of an adhesive sheet.

In addition, in the case of the resin board 50 made of a prepreg, sincethe resin which is contained has adhesive properties, recesses 51 can becreated in the resin of the surface layer without forming an adhesivelayer. The recesses 51 can be created in a similar manner by using theabove described support body or metal mold.

In addition, in the case of a prepreg, recesses 51 can be createdthrough a conventional manufacturing step. That is to say, in amanufacturing process for a resin board 50 using a prepreg, first, areinforcing material in a sheet form such as a glass cloth or aramidpaper is soaked in a solution distilled by a solvent so as to have thedesired viscosity and, thereby, a resin board 50 is manufactured. Then,an extra solution is removed from the manufactured resin board 50 bymeans of a roller, or the like, and, in addition, the board is dried inorder to remove the extra solvent. In such a processing step, the resinboard 50, before being dried, is passed through a roller which isprovided with protruding parts corresponding to the recesses 51.Thereby, the resin board 50 which has recesses 51 on the surface can beeasily manufactured.

In addition, in a manufacturing process for a resin board 50 by using aprepreg, recesses 51 can be created as follows. That is to say, theboard undergoes sudden heating and drying treatments in the drying stepfor removing the extra solvent. Thereby, holes are created, after thesolvent has been removed therefrom, in the surface of the resin board 50and these holes become the recesses 51.

As an example of such a manufacturing process, there is the followingmethod. That is to say, an MEK (methyl-ethyl-ketone) solution (60%solids) of an epoxy resin composition for prepreg impregnation isimpregnated in an aramid non-woven cloth (basis weight of 72 g/m², 120μm thick) and, thereby, a resin board 50 is manufactured. Then, theresin board 50 is passed between a pair of rollers which have a gap of150 μm and, thereby, an extra solution is squeezed out from the resinboard 50. After that, the resin board 50 is placed in a dryer which isheated to 200° C. for three minutes. Thereby, recesses 51 are created inthe resin board 50.

According to this method no extra steps are necessary for providing therecesses 51 so that the resin board 50 can be inexpensivelymanufactured.

In the case of the resin board 50 of the present embodiment wherein anadhesive layer is formed on one side or on both sides of a film board,recesses 51 can be created. That is to say, in the step of drying afterapplying an adhesive layer, holes are caused by suddenly heating anddrying the board in the same manner as in the above so that recesses 51are created in the resin board 50.

Fourth Preferred Embodiment

Next, a structure of a medium connection body 12 used in the resinboards 10A, 10B, 30 and 50, described in the first to the thirdpreferred embodiments, is described in reference to FIG. 5. Here, in theconnection medium body 12 described in the present embodiment inreference to FIG. 5 or in the circuit board described in the belowdescribed embodiment, any of the resin boards 10A, 10B, 30 and 50 can beused as a resin board. Therefore, the resin boards 10A, 10B, 30 and 50are generally referred to as a resin board 10 in the description belowor in the figures referred to in the description. In addition, since theporous layer 11, the insulating particle layer 32 or the recesses 51 allfunction as compression function layers, the porous layer 11, theinsulating particle layer 32 or the recesses 51 are all referred to ascompression function layer 60 in the description below or in the figuresreferred to in the description.

The medium connection body 12 is formed by creating through holes 13 indesired positions of a resin board 10 and, after that, by filling thesethrough holes 13 with conductors 14 as shown in FIG. 5. The conductors14 become interstitial via holes.

As for the conductors 14, conductive paste which contains conductivepowder in a resin binder can be used. The conductive paste increases itsconductivity through the application of compression.

As for the conductive powder, a powder is used made of, at least, onetype of metal selected from among gold, silver, copper, nickel,palladium, lead, tin, indium and bismuth, an alloy of these or a mixtureof these. In addition, coat fillers made by coating spheres made of themetal or alloy, oxides such as alumina or silica or organic synthesizedresin with the above described metal or alloy may be used as theconductive powder.

The form of the conductive powder is not particularly limited and may bea powder, a fiber, granules, spherical balls, or a mixture of these.

As for the resin used as the resin binder, an epoxy resin in a liquidform, a polyimide resin, a cyanate ester resin, a phenol resol resin, orthe like, is used.

As for the epoxy resin, a glycidyl-ether-type epoxy resin such as abisphenol-A type epoxy resin, a bisphenol-F type epoxy resin or abisphenol-AD type epoxy resin or an epoxy resin which has two, or more,epoxy groups such as an alicyclic epoxy resin, a glycidyl-amine-typeepoxy resin, a glycidyl-ester-type epoxy resin, or the like, is used.

An additive of a solvent or a dispersion agent such as butyl-cellosolve,ethyl-cellosolve, butyl-carbitol, ethyl-carbitol,butyl-carbitol-acetate, ethyl-carbitol-acetate and α-terpineol can, ifnecessary, be contained in the above described resin.

In addition, the conductors 14 are not limited to the above describedconductive paste but, rather, a connection material for interstitial viaholes of the type which can gain conductivity through contact by beingcompressed such as via posts made of a metal such as gold, silver,copper, nickel, palladium, lead, tin, indium and bismuth can be usedwithout a particular limitation.

In the creation of the interstitial via holes in the connection mediumbody 12, first, through holes 13 are created in desired positions of theresin board 10. As for the method for creating the through holes 13, aconventional hole processing method for circuit boards, a laserprocessing method by using a carbonic acid gas laser or a YAG laser or amechanical processing method such as drilling or punching can be used.

In particular, in the case that through holes 13 are created by means ofa heat processing laser processing method, the surrounding walls of thethrough holes 13 can be melted. At this time, in the case that thecompression function layer 60 is formed of the porous layer 11, itbecomes as follows. That is to say, holes 104 of the porous layer 11positioned in the surrounding walls disappear due to the melting of thesurrounding walls of the through holes. The holes 104 positioned in thesurrounding walls of the through holes can become places into whichleaking occurs at the time when the conductive paste filled in withinthe through holes leaks into the surrounding area. Therefore, when theholes 104 of these places are made to disappear, the paste can beprevented from leaking.

However, it is not necessary to completely compress the holes 104. Theholes 104 may be compressed to a size such that the conductive powderdoes not enter into the holes and, thereby, above-described effect ofpreventing the paste from leaking can be gained and, in addition, thefollowing effect can be gained. That is to say, in the above case resincomponents in the conductive paste enter into the holes 104 which areallowed to remain in the condition where they become smaller and, as aresult, the compression of the conductive paste filled into the throughholes 13 is increased so that the resistance of the conductive paste(conductors 14) can be lowered.

Next, conductors 14 are filled into the through holes 13 so that theconnection medium body 12 shown in FIG. 5 is completed.

A printing method is used in order to fill in the conductors 14. At thistime, a resin board 10 in which through holes 13 are created is placedon a vacuum absorption support via a sheet of paper so that theconductors 14 are filled in through printing. Then, when the connectionmedium body 12 is compressed during the below described manufacturingstep for a circuit board, the density of the conductive particles filledin can be further increased. This is because resin components in theconductive paste 14 are forcefully absorbed into the sheet of paper dueto absorption by vacuuming and due to capillary action caused in thesheet of paper and, thereby, the density of the conductive powder filledin is enhanced and gaps are caused among conductive powder particles.

Fifth Preferred Embodiment

Next, the structure of a circuit board using the connection medium body12 described in the fourth preferred embodiment and the manufacturingprocess thereof are described. First, a manufacturing process for atwo-sided circuit board 17 is described in reference to FIG. 6.

As shown in FIG. 6A, metal foils 15 for forming wiring layers areoverlapped on both sides of the connection medium body 12, which isheated and compressed for adhesion. The conditions for the adhesionthrough heating and compression differ depending on the structure of theutilized material. For example, in the case that the resin substrate 10wherein an adhesive layer 102 (approximately 6 μm thick) made of apolyimide-based resin is formed on the resin board 10 made of apolyimide film board (13 μm thick), the board is heated and iscompressed for one hour at pressure of 50 kgf/cm² and at a temperatureof 200° C.

As for the metal foils 15, copper foils such as an electrolytic copperfoil or a rolled copper foil used for a conventional circuit board areused. Though the thickness of the metal foils 15 are not particularlylimited, an electrolytic copper foil of 3 μm to 70 μm is readilyavailable and is preferable.

In the above described processing steps, metal foils 15 and theconnection medium body 12 are adhered through heating and compression.Next, as shown in FIG. 6B, the metal foils 15 are processed into wiringlayers 16 which have desired wiring patterns. Thereby, the two-sidedcircuit board 17 is completed. As for the processing of the wiringlayers 16, a photolithographic method, which is used in a conventionalcircuit board manufacturing, can be used.

In such a manufacturing process for a two-sided circuit board 17, at thetime when the metal foils 15 undergo heating and compression processing,the connection medium body 12 is compressed so that the thicknessthereof becomes thinner due to the function of the compression functionlayer 60. Thereby, the conductors 14 are simultaneously compressed,together with the compression of the connection medium body 12, so thatthe conductivity thereof is enhanced.

First, a compression addition in the case where the compression functionlayer 60 is formed of the porous layer 11 is described. In this case,the resin components of the surface portions of the resin board 10 havefluidity and, therefore, pressure is applied to connection medium body12 in the direction of the thickness and the above described resincomponents are impregnated into a hole group 103 within the porous layer11 so that the porous layer 11 sinks into the resin board 10B and of theconnection medium body 12 is compressed so that the thickness becomesthinner by the amount of sinkage. Thereby, the conductors 14 aresimultaneously compressed, together with the compression of theconnection medium body 12, so that the conductivity thereof is enhanced.

Next, a compression addition in the case that the compression functionlayer 60 is formed of the insulating particle layer 32 is described. Inthis case, insulating particles 31 are pressed into the inside of theadhesive layer 102′ in the heating and compression step. Thereby, theresin board 30 is compressed and the thickness of the connection mediumbody 12 becomes thinner by the amount of compression. Thereby, theconductors 14 are simultaneously compressed together with thecompression of the connection medium body 12 so that the conductivitythereof is enhanced.

Next, a compression addition in the case that the compression functionlayer 60 is created from the recesses 51 is described. In this case, therecesses 51 disappear in the heating and compression step. Thereby, theresin board 50 is compressed and the thickness of the connection mediumbody 12 becomes thinner by the amount of compression. Thereby, theconductors 14 are simultaneously compressed together with thecompression of the connection medium body 12 so that the conductivitythereof is enhanced. That is to say, as shown in FIGS. 7A and 7B, therecesses 51, into which the resin components 52 flow into from thesurrounding areas, carries out the function of compressing theconnection medium body 12 (resin board 50). In this case, it isimportant to control the entire volume of the recesses 51. In detail,the ratio of the entire volume of the recesses 51, which is occupied inthe connection medium body 12, to the entire volume of the connectionmedium body 12 (entire volume of recesses 51/entire volume of connectionmedium body 12) is required to be equal to the compression ratio of theconnection medium body 12.

It is preferable to set the compression ratio of the conductors 14 asfollows. That is to say, in the case that the conductors 14 are used asinterstitial via holes, a compression ratio of 5%, or higher, ispreferable. It is possible to secure the conductivity of theinterstitial via holes with a compression ratio of less than 5%.However, in the case of 5%, or higher, a sufficient pressure is appliedto the contact portions among conductive powder particles as well as tothe contact portions between the conductive powder particles and themetal foils 15 so as to ensure strong adhesion. Thereby, the connectionresistance of the interstitial via holes is lowered. In addition, thestability of the connection is increased.

The two-sided circuit board 17 manufactured in this manner has thefollowing structure. That is to say, the resin board 10 has thecompression function layer 60 on, at least, one board surface. The resinboard 10 has through holes 13 in the thickness direction. Conductors 14are filled into the through holes 13. Wiring layers 16, which havedesired wiring patterns, are provided on both sides of the resin board10. The wiring layers 16 on both sides of the resin board 10 areelectrically connected to each other through the conductors 14.

In the case that the two-sided circuit board 17 is formed, the followingis preferable. That is to say, as shown in FIG. 8, it is preferable tomake the maximum diameter L of the holes 104, which are components ofthe hole group 103, smaller than the minimum separation interval S ofthe conductors 14. In this manner it becomes as follows.

The conductive paste forming the conductors 14 invades into holes 104 byreceiving pressure and a short circuit among the conductors 14, due tothe conductive paste which has invaded into the holes 104, can beprevented by setting the maximum diameter L as described above.

In the present embodiment, by combining the compression addition effectof the compression function layer 60 and another technology, thecompression power can be further enhanced.

For example, during the step of heating and compression the resin board10, with the metal foils 15 being overlapped, wiring layers 16, whichare formed in advance, are pressed into the connection medium body 12instead of the metal foils 15, that is to say, a so-called transcriptionmethod is used.

In detail, as shown in FIG. 9, a so-called wire layer with carrierwherein a wiring layer is formed on a support board 20 can be used. Asan example of a wiring layer with carrier, there is an aluminum carrieron which a wiring layer is layered via a mold releasing layer.

That is to say, as shown in FIG. 9A, a wiring layer 21 is formed byetching a copper foil layered and placed on the support board 20 forpatterning by using a ferric chloride solution, an ammonium persulfatesolution, or the like. Then, as shown in FIGS. 9A and 9B, after layeringthe wiring layer 21 so as to be buried in the connection medium body 12,the support body 20 is removed through etching by means of hydrochloricacid.

By using a transcription method, the pressure applied to the conductors14 in the connection medium body 12 becomes the sum of the pressure dueto the porous layer 11 and the pressure due to the pressed in wiringlayer 21.

In addition, by using a compressible base material within which thereare holes as the resin board 10′, a greater pressure can be applied tothe conductors 14 due to the synergetic effects with compressionaddition effect of the porous layer 11 according to the presentinvention. As for such a resin board 10′, a porous film of polyimide orof fluorine resin can be cited.

In addition, as shown in FIG. 10, by making the conductors 14 filledinto the through holes 13 protrude from the surface of the connectionmedium body 12, the pressure applied to the conductors 14 throughheating and compression can be further enhanced. This is described inthe following.

First, as shown in FIG. 10A, a protective film layer 22 made of a filmmaterial such as PET (polyethylene-terephthalate), PEN(polyethylene-naphthalate), or the like, and upon which is carried out amold releasing process (for example, a process using a silicon-basedmold releasing agent), is attached to the surface which the boardcontacts, is attached to, at least, one surface of the resin board 10which has the compression function layer 60. In the case that theprotective film layer 22 is formed of these materials, the protectivefilm layer 22 can be attached to the resin board 10 so as to beremovable.

Next, as shown in FIG. 10B, through holes 13 are created in the resinboard 10, which includes the protective film layer 22. Then, through aprinting method conductors 14 are filled into the through holes 13. Atthis time the protective film layer 22 works as a mask which preventsthe conductors 14 from becoming attached to undesirable portions.Furthermore, the conductors 14 which are filled into the through holes13 are increased in size by the thickness of the protective film layer22.

Next, as shown in FIG. 10C, when the protective film layer 22 isremoved, the connection medium body 12 wherein the conductors 14protrude from the through holes 13 is gained. Metal foils 15 areattached to both sides of the resin board 10 in this condition. Then,the metal foils 15 and the resin board 10 are integrated by adhesionthrough heating and compression. At this time, the conductors 14protrude from the through holes 13 and, thereby, the portions of theconductors 14 which protrude work during heat compression step so as toenhance the pressure to the conductors 14.

Finally, by patterning the metal foils 15 in the photolithographic step,the metal foils 15 are converted to the wiring layers 16 which havedesired wiring patterns. Thereby, the two-sided circuit board 17 shownin FIG. 10D is gained. In this two-sided circuit board 17 the connectionreliability of the interstitial via holes is enhanced to a degree equalto the enhanced pressure applied to the conductors 14.

In the above manner, the connection medium body 12 or the two-sidedcircuit board 17 are formed and in the case that a multi-layer circuitboard is manufactured by using these connection medium body 12 or thetwo-sided circuit board 17, the process becomes as follows.

As shown in FIG. 11A, the above described two-sided circuit board 17 ora core board 18 made of a conventional two-sided circuit board such as aglass epoxy board is prepared. Then, the connection medium body 12 isoverlapped on the wiring layer 16 of the prepared core board 18 and ametal foil 15 is overlapped on top of that so as to be adhered throughheating and compression. Thereby, the core board 18, the connectionmedium body 12 and the metal foil 15 are integrated. Here, it ispreferable to use the connection medium body 12 wherein conductors 14slightly protrude from the medium body surface. Thus the pressureapplied to the conductors 14 can be further enhanced.

Furthermore, the metal foil 15 is processed into the wiring layer 16 bymeans of photolithographic method. Thereby, the multi-layer circuitboard shown in FIG. 11B is completed. Here, by repeating this method, anumber of layers of a circuit board can be easily manufactured.

Next, another manufacturing process for a two-sided circuit board or amulti-layer board is described in reference to FIGS. 12 and 13.

First, a resin board 10 wherein a compression function layer 60 isattached to at least one board surface and a wiring layer 21 which issupported by a support board 20 are prepared. Then, a protective filmlayer 22 is attached to one board surface of the resin board 10. Here,the protective film layer 22 may be provided on the surface on which thecompression function layer is placed or may be provided on the surfaceon which the compression function layer is not placed. In FIG. 12, as anexample, the protective film layer 22 is provided on the surface onwhich the compression function layer is placed.

Next, as shown in FIGS. 12A-1 and 12A-2, a wiring layer 21 is placed onthe surface on which the protective film layer is not placed of theresin board 10. At this time, the wiring layer 21 is positioned withrespect to the resin board 10 before it is placed on the board. Here, asshown in FIG. 12A-2, the wiring layer 21 may be placed in the conditionwhere it is partially sunk into the resin board 10 through a compressionprocess. Contrarily, as shown in FIG. 12A-1, the wiring layer 21 may beplaced in the condition where it rests on the surface of the resin board10 without carrying out a compression process. In the case that thewiring layer 21 is placed on the resin board 10 in the condition whereit rests on the board surface, the wiring board 21 will be made to sinkinto the resin board 10 through the below described heat compressionstep and at that time, the pressure applied to the conductors 14 can beenhanced.

Next, through holes 13 are created in the resin board 10. The throughholes 13 are created in the direction of the thickness so as to reach tothe wiring layer 21 starting from the surface on which the protectivefilm layer is placed. At this time, the through holes 13 are created inthe condition where they are positioned with respect to the wiring layer21. The through holes 13 can be created by means of a laser processingmethod using a carbonic acid gas laser, a YAG laser, an excimer laser,or the like. In particular, in the case that the through holes 13 arecreated by means of heat processing laser processing method, thesurrounding walls of the through holes 13 can be melted. At this time,in the case that the compression function layer 60 is formed of a porouslayer 11, it becomes as follows. That is to say, holes 104 of the porouslayer 11 positioned in the surrounding walls disappear due to themelting of the surrounding walls of the through holes. The holes 104positioned in the surrounding walls of the through holes can becomeplaces into which leaking occurs at the time when the conductive pastefilled in within the through holes leaks into the surrounding area.Therefore, when the holes 104 of these places are made to disappear, thepaste can be prevented from leaking.

However, it is not necessary to completely compress the holes 104. Theholes 104 may be compressed to a size such that the conductive powderdoes not enter into the holes and, thereby, above-described effect ofpreventing the paste from leaking can be gained and, in addition, thefollowing effect can be gained. That is to say, in the above case resincomponents in the conductive paste enter into the holes 104 which areallowed to remain in the condition where they become smaller and, as aresult, the compression of the conductive paste filled into the throughholes 13 is increased so that the resistance of the conductive paste(conductors 14) can be lowered.

After creating the through holes 13, as shown in FIG. 12B, conductors 14made of conductive paste are filled into the through holes 13. At thetime of the filling in of the conductors 14, in the case that a pressurereduction treatment is applied to the through holes 13 at the time ofthe filling in or after the filling in, bubbles can be prevented fromremaining within the through holes. Such a pressure reduction treatmentleads to the high density filling in of the conductors 14.

After filling in the conductors 14, the protective film layer 22 isremoved. Then, as shown in FIG. 12C, a metal foil 15 is placed on thesurface of the resin board 10 from which the protective film layer hasbeen removed and an adhesion treatment through heating and compressionis applied. As for the condition of the adhesion treatment throughheating and compression, the conditions of the adhesion treatmentthrough heating and compression for a conventional circuit board can beused. For example, the conditions of 180° C. to 250° C., 30 kgf/cm² to200 kgf/cm², 0.5 hours to 2.0 hours can be used.

Finally, the metal hole 15 is processed to a wiring layer 16 which hasdesired wiring patterns by means of a photolithographic method. Then,the support board 20 is removed. Thereby, the two-sided wiring board 17shown in FIG. 12D is completed.

Since the conductors 14 can be formed according to the position of thewiring layer 16 in the above method, the positioning precision betweenthe wiring layer 16 and the conductors 14 is increased.

In the case that a multi-layer board is formed, it is manufactured asfollows.

First, a layered body shown in FIG. 13A is manufactured. This is gainedby replacing the wiring layer 21 with a support board with the two-sidedcircuit board 17 shown in FIG. 12D in the structure of the resin board10 with a wiring layer shown in FIGS. 12A-1 and 12A-2.

Then, a metal foil 15 is layered on the manufactured layered body. Themetal foil 15 is placed on the surface of the layered body on which awiring layer is not placed.

After placing the metal foil 15 on the above described layered body, thelayered body undergoes an adhesion treatment through heating andcompression. Then, the metal foil 15 is processed to a wire layer 16which has desired wiring patterns by means of a photolithographicmethod. Thereby, a multi-layer board shown in FIG. 13B is gained.Furthermore, by repeating the above described steps, a circuit board ofan increased number of layers can be manufactured.

Still another manufacturing process for a circuit board is described inreference to FIGS. 14 and 15.

First, a resin board 10 wherein a compression function layer 60 and aprotective film layer 22 are attached to at least one board surface anda core board 18 shown in FIG. 11A are prepared. Then, a layered body isformed by placing and layering the resin boards 10 on both sides of thecore board 18. Here, the resin boards 10 are layered as follows. That isto say, the protective film layer 22 is removed from the surface of theresin board 10 which will contact the core board before the resin board10 is layered on the core board 18. Or the resin board 10 is layered onthe core board 18 in the condition that the resin board 10 is placed inthe direction where the surface on which the protective film layer isnot formed contacts the two-sided circuit board 17.

Then, as shown in FIGS. 14A and 14B, through holes 13 are created in therespective resin boards 10 which are placed and layered on the coreboard. The through holes 13 are created in the condition where they arepositioned with respect to the wiring layers 16 which lay on the bottomsof the through holes. That is to say, the through holes 13 are createdin the direction of the thickness of the resin boards 10 so as to reachto the wiring layers 16.

After creating the through holes 13, as shown in FIGS. 14C and 15A,conductors 14 are filled into respective through holes 13. After that,the protective film layers 22 are removed.

After removing the protective film layers 22, metal foils 15 (not shown)are placed on both sides of this layered body. Then, by making thelayered body undergo an adhesion treatment through heating andcompression, the layered body and the metal foils 15 are integrated.Finally, the metal foils 15 are processed into wiring layers 16 whichhave desired wiring patterns by means of a photolithographic method.Thereby, the multi-layer board shown in FIG. 15B is completed.

Next, the reason why it is advantageous in a structure of a circuitboard to provide a compression function layer of the present invention,represented by the porous layer 11, is described.

First, the first reason is described. In a board structure whereininterlayer connections are made of conductors, which are made ofconductive paste, it is essential to compress the conductors in somefashion. Conventionally, a prepreg having holes inside is used as theresin board and this prepreg is compressed so as to compress theconductors. That is to say, by applying pressure to the prepreg, theholes are crashed so as to shrink the dimension of the prepreg in thethickness direction and, thereby, the conductors are compressed.

In the case that a large number of holes exist inside of the resinboard, however, dimensional change easily occurs due to temperaturechange, moisture change or external force. It is desirable for thedimensional change during a manufacturing step for a circuit board to beas small as possible because it is a cause of processing step defectssuch as pattern shift. In this manner, holes created in the resin boarditself become a factor that causes the circuit board easily change inform, which is disadvantageous in a manufacturing step for a circuitboard that requires a higher density and a higher precision in wiring.

Contrarily, as for the resin board 10 of the present invention wherein acompression function layer 60 such as a porous layer 11 is provided on asurface, the board itself can be formed of a resin in a solid condition(condition with non holes) and, therefore, the dimension change can bereduced and a higher density of the circuit board can be sufficientlyachieved.

Next, the second reason is described. The higher the density is made inthe circuit board, the narrower become the separation intervals betweenthe conductors. As described above in reference to FIG. 8, in the casethat holes exist among the conductors and the maximum diameter of theholes is larger than the minimum separation interval between theconductors, adjoining conductors may be short-circuited by theconductive paste which has invaded into a hole.

However, it is not easy to highly precisely control the size of theholes in a prepreg and, in particular, it is difficult to createmicroscopic holes in a highly precise manner. Therefore, in theconfiguration of a circuit board to which a compressibility is given bycreating holes in a prepreg, it becomes more difficult to make thediameter of the holes smaller than the separation intervals amongconductors as the density of mounting becomes higher. As a result, therisk of short-circuit between conductors due to the conductive pasteinvading into a hole increases in a circuit board of which the densityhas been made higher. In this manner, the creation of holes in the resinboard is not acceptable because as the density of mounting becomeshigher, short-circuits are increasingly caused.

Contrarily, in a resin board 10 of the present invention where acompression function layer 60 (in particular, porous layer 11) isprovided on a surface, the sizes of holes 104 can be controlled in ahighly precise manner so that microscopic holes 104 can be created in ahighly precise manner. Therefore, by providing a porous layer 11 whichhas such holes 104, a short-circuit due to the conductive paste invadinginto the holes 104 can be prevented even in the case that the density ofmounting has become higher in the circuit board.

In addition, in the case that the porous layer 11 is provided, themechanical strength of the resin board 10 can be reinforced.

As described above, according to the present invention, advantageouseffects can be gained that a resin board and a connection medium bodyprovided with a low connection resistance of inner via holes and anexcellent connection stability as well as a circuit board using theabove resin board or connection medium body can be implemented.

Though this invention is described in detail with respect to the mostpreferred embodiment thereof, the combination and arrangement of thecomponents in the preferred embodiment can be modified in a variety ofmanners without deviating from the spirit and the below claimed scope ofthis invention.

What is claimed is:
 1. A resin board for use as an insulating layer of acircuit board, wherein: a compression function layer is provided on atleast one board surface and this compression function layer adds afunction of being compressed by receiving pressure in the direction ofthe board thickness to the resin board which includes the layer, saidcompression function layer is a porous layer, said porous layer having ahole group formed of a plurality of holes which are connected to eachother and both edges of the hole group have openings on both sides ofthe porous layer.
 2. The resin board according to claim 1, wherein saidcompression function layer is a layer of insulating particles providedin this resin board in the condition of protruding from the boardsurface.
 3. The resin board according to claim 1, wherein the resinboard is in a semi-cured condition at least on the surface on which thecompression function layer is provided.
 4. The resin board according toclaim 1, wherein a protective film layer that is removable is providedas an additional layer above said compression function layer.
 5. Theresin board according to claim 1, further comprising a metal filmdisposed on at least a portion of said compression function layer.
 6. Aconnection medium body for being provided between two wiring layers thatare placed so as to face each other and for electrically connectingthese wiring layers, comprising: a resin board; a compression functionlayer is provided on at least one board surface of said resin board,said compression function layer is a porous layer, said porous layerhaving a hole group formed of a plurality of holes which are connectedto each other and both edges of the hole group have openings on bothsides of the porous layer; through holes created in he direction of thethickness of said resin board; and conductors provided in said throughholes, wherein said compression function layer adds a function of beingcompressed by receiving pressure in the direction of the thickness tothe connection medium body which includes this layer.
 7. The mediumconnection body according to claim 6, wherein said compression functionlayer is a layer of insulating particles provided in said resin board inthe condition of protruding from the board surface.
 8. The mediumconnection body according to claim 6, wherein the resin board is in asemi-cured condition at least on the surface on which the compressionfunction layer is provided.
 9. The medium connection body according toclaim 6, wherein at least one of said wiring layers is disposed on atleast a portion of said compression function layer.
 10. A connectionmedium body for being provided between two wiring layers that are placeds as to face each other and for electrically connecting these wiringlayers, comprising: a resin board; a porous layer provided n at leastone board surface of said resin board, said porous layer having a holegroup formed of a plurality of holes which are connected to each otherand both edges of the hole group have openings on both sides of theporous layer; through holes created in the direction of the thickness ofsaid resin board; and conductors provided in said through holes.
 11. Themedium connection body according to claim 10, wherein at least one ofsaid wiring layers is disposed on at least a portion of said porouslayer.
 12. A circuit board, comprising: a resin board; a compressionfunction layer provided on at least one board surface of said resinboard, said compression function layer is a porous layer, said porouslayer having a hole group formed of a plurality of holes which areconnected to each other and both edges of the hole group have openingson both sides of the porous layer; through holes created in he directionof the thickness of said resin board; conductors provided in saidthrough holes; and wiring layers which are provided on both sides ofsaid resin board and which are electrically connected to each other viasaid conductors, wherein said compression function layer is compressedby receiving pressure in the board direction of the thickness to theresin board which includes the layer.
 13. The circuit board according toclaim 12, wherein the size of the holes of said porous layer is smallerthan the minimum separation interval of adjoining said through holes.14. The circuit board according to claim 12, wherein said compressionfunction layer is a layer of insulating particles provided in this resinboard in the condition of protruding from the board surface.
 15. Thecircuit board according to claim 12, wherein at least one of said wiringlayers is disposed on at least a portion of said compression functionlayer.
 16. The circuit board according to claim 12, wherein a resincomponent invades into holes of said porous layer so as to subduct saidporous layer in a resin board.
 17. A circuit board, comprising: a resinboard; a porous layer provided on at least one board surface of saidresin board, said porous layer having a hole group formed of a pluralityof holes which are connected to each other and both edges of the holegroup have openings on both sides of the porous layer; through holescreated in he direction of the thickness of said resin board; conductorsprovided in said through holes; and wiring layers which are provided onboth sides of said resin board and which are electrically connected toeach other via said conductors.
 18. The circuit board according to claim17, wherein at least one of said wiring layers is disposed on at least aportion of said porous layer.